The geometry of flow trace is of significance in detecting early atherosclerotic changes, as is the assessment of perfusion levels. Since arterial compliance is relatively linear over a local pulse pressure range, the geometries of the pulse volume and pulse pressure contours are quite similar. In essence, however, the pulse volume recording is a segmental volume-time tracing. If one differentiates the volume-time curve, a calibrated flow-time curve is obtained, representing the pulsatile component of the total flow.
The known art includes well developed devices for obtaining the above information in displayed and recorded form. However, because the detection of pulses at various locations on the body of a patient is essentially mechanical, unexpected movement of the patient during periods of measurement can cause a shifting of the electrical baseline which forms the ordinate against which the obtained curve is plotted. Miscellaneous electrical noise can have the same effect, although normally to a lesser degree. Prior art devices have failed to incorporate means for compensating against baseline shift, and as a result have produced output signals which are difficult to evaluate.